[Windows] Fix issue with caching the page that holds unfocused control

src/Controls/tests/DeviceTests/Elements/Entry/EntryTests.cs

@@ -1,7 +1,9 @@
 using System;
 using System.Threading.Tasks;
 using Microsoft.Maui.Controls;
+using Microsoft.Maui.DeviceTests.Stubs;
 using Microsoft.Maui.Handlers;
+using Microsoft.Maui.Hosting;
 using Xunit;
 
 namespace Microsoft.Maui.DeviceTests
@@ -52,6 +54,50 @@ await InvokeOnMainThreadAsync(() =>
 				Assert.True(platformControl.IsReadOnly);
 			});
 		}
+
+
+		[Fact(DisplayName = "Unfocus will work when page is shown a 2nd time")]
+		public async Task UnFocusOnEntryAfterPagePop()
+		{
+			int unfocused = 0;
+			EnsureHandlerCreated(builder =>
+			{
+				builder.ConfigureMauiHandlers(handlers =>
+				{
+					handlers.AddHandler(typeof(Toolbar), typeof(ToolbarHandler));
+					handlers.AddHandler(typeof(NavigationPage), typeof(NavigationViewHandler));
+					handlers.AddHandler<Page, PageHandler>();
+					handlers.AddHandler(typeof(Window), typeof(WindowHandlerStub));
+					handlers.AddHandler(typeof(Entry), typeof(EntryHandler));
+
+				});
+			});
+
+			var entry = new Entry();
+			entry.Unfocused += (s, e) =>
+			{
+				if(!e.IsFocused)
+				{
+					unfocused++;
+				}
+
+			};
+			var navPage = new NavigationPage(new ContentPage { Content  = entry });
+			var window = new Window(navPage);
+
+			await CreateHandlerAndAddToWindow<WindowHandlerStub>(window, async (handler) =>
+			{
+				entry.Focus();
+				await Task.Delay(500);
+				entry.Unfocus();
+				await navPage.PushAsync(new ContentPage());
+				await navPage.PopAsync();
+				entry.Focus();
+				await Task.Delay(500);
+				entry.Unfocus();
+				Assert.True(unfocused == 2);
+			});
+		}
 #endif
 
 		[Theory(DisplayName = "CursorPosition Initializes Correctly")]

src/Core/src/Platform/Windows/ViewExtensions.cs

@@ -19,8 +19,6 @@ namespace Microsoft.Maui.Platform
 {
 	public static partial class ViewExtensions
 	{
-		internal static Page? ContainingPage; // Cache of containing page used for unfocusing
-
 		public static void TryMoveFocus(this FrameworkElement platformView, FocusNavigationDirection direction)
 		{
 			if (platformView?.XamlRoot?.Content is UIElement elem)
@@ -368,34 +366,33 @@ internal static void UnfocusControl(Control control)
 			// hack. What we *can* do is set the focus to the Page which contains Control;
 			// this will cause Control to lose focus without shifting focus to, say, the next Entry 
 
-			if (ContainingPage == null)
-			{
-				// Work our way up the tree to find the containing Page
-				DependencyObject parent = control;
-
-				while (parent != null && parent is not Page)
-				{
-					parent = VisualTreeHelper.GetParent(parent);
-				}
+			// Work our way up the tree to find the containing Page
+			// We can't cache this parent because this Page can be disposed
+			// or the Control can belong to another page
+			DependencyObject parent = control;
 
-				ContainingPage = parent as Page;
+			while (parent != null && parent is not Page)
+			{
+				parent = VisualTreeHelper.GetParent(parent);
 			}
 
-			if (ContainingPage != null)
-			{
-				// Cache the tabstop setting
-				var wasTabStop = ContainingPage.IsTabStop;
+			if (parent is not Page containingPage)
+				return;
 
-				// Controls can only get focus if they're a tabstop
-				ContainingPage.IsTabStop = true;
-				ContainingPage.Focus(FocusState.Programmatic);
+			// Cache the tabstop setting
+			var wasTabStop = containingPage.IsTabStop;
 
-				// Restore the tabstop setting; that may cause the Page to lose focus,
-				// but it won't restore the focus to Control
-				ContainingPage.IsTabStop = wasTabStop;
-			}
+			// Controls can only get focus if they're a tabstop
+			containingPage.IsTabStop = true;
+			containingPage.Focus(FocusState.Programmatic);
+
+			// Restore the tabstop setting; that may cause the Page to lose focus,
+			// but it won't restore the focus to Control
+			containingPage.IsTabStop = wasTabStop;
 		}
 
+
+
 		internal static IWindow? GetHostedWindow(this IView? view)
 			=> GetHostedWindow(view?.Handler?.PlatformView as FrameworkElement);